A technique that forms a composite image from two photographed images of one object is known as a technique for improving the quality of a photographed image (for example, see Patent Literature 1).
In the technique described in Patent Literature 1 (hereinafter, referred to as “conventional technique”), a composite image is formed through superimposition of pixel values from a short-exposure image and the respective pixel values from a long-exposure image of one object for individual pixel pairs. In this operation, the conventional technique increases the percentage of the pixel value of the short-exposure image to adjust a blurring range of an edge of an object in the long-exposure image. The short-exposure image has many noises but has a clear edge. The long-exposure image has an unclear edge but has few noises. As a result, the conventional technique achieves formation of a composite image that exhibits both the advantages of the short-exposure image and the long-exposure image while doubling the total dynamic range over the pixel values.